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Title: Engineering cyanobacterial genes into Glycine max (soybean) leads to increased photosynthesis and productivity
Author(s): Hay, William
Director of Research: Long, Stephen P.
Doctoral Committee Chair(s): Long, Stephen P.
Doctoral Committee Member(s): Ort, Donald R.; Clough, Steven J.; Bernacchi, Carl J.
Department / Program: School of Integrative Biology
Discipline: Biology
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Photosynthesis
ictB
SBPase
FBPase
mesophyll conductance
photorespiration
Rubisco
fluorescence
crop improvement
free air gas concentration enrichment (FACE)
Abstract: The rise in global population, increasing economic status in the developing world, reduction in arable land and increase in extreme weather all pose serious problems to sustaining sufficient food production to meet the ever increasing demand. With yields per unit land area failing to increase to match the rising demand, rapid improvements in plant productivity will be necessary. This thesis aimed to discover whether two novel cyanobacterial genes that putatively increase photosynthesis are able to improve photosynthesis and productivity in soybean, the world’s fourth most produced food crop. Glycine max [L.] Merr cv. Thorne were transformed with the two cyanobacterial genes, ictB and FBP1, and first examined under controlled greenhouse conditions and then over two years of field trials in current and future [CO2] (585-590 μmol mol-1) to determine the potential of improving an already highly productive C3 crop species. The ictB gene was expected to facilitate bicarbonate transfer across the plastid membrane, thereby increasing [CO2] within the stroma and at the site of RuBP carboxylase/oxygnease (Rubisco). In the greenhouse study, the G. max expressing the ictB gene showed increases of 10% in the in vivo rate of RuBP- (ribulose-1:5-bisphosphate) limited photosynthesis, 9% in RuBP-saturated photosynthesis, and 24% in mesophyll conductance to CO2. Importantly, the final plant mass increased by 13%, and seed yield by 15%. Consistent with the greenhouse experiment, the ictB line in the two year field trials showed higher rates of light-saturated leaf CO2 uptake of 15% in ambient [CO2] relative to wild type. The elevated [CO2] had an additive effect on photosynthesis and productivity in the ictB line, showing an increased rate of light-saturated CO2 uptake of 25% and increased seed yield of 27% compared to wild type in elevated [CO2]. The ictB line showed a significant increase in the maximum quantum yield of CO2 uptake, strongly suggesting that ictB acts to increase passive diffusion of inorganic carbon to Rubisco. The FBP1 gene encodes the FBPase/SBPase bifunctional enzyme which has the same enzymatic function as the two individual enzymes present in higher plants. These two enzymes regulate key steps in the reductive pentose-phosphate (Calvin) cycle, the primary pathway for carbon fixation in higher plants. G. max plants expressing the FBP1 gene only showed increased photosynthesis and productivity when grown in the open-air field trails. The FBP1 line, G. max expressing the FBP1 gene, had increased photosynthesis when grown in elevated [CO2] consistent with the hypothesis that expression of the FBP1 gene would increase capacity for RuBP-regeneration at elevated [CO2], showing 16% higher rates of leaf photosynthetic CO2 uptake (Asat) and a 11% increased maximum rate of electron transport (Jmax). The FBP1 line also exhibited a 10.5% increase in seed yield per hectare, likely due to an increase in the number of nodes and pods. Increases in yield were also likely due to a significant extension of seed fill in the FBP1 line. The research presented in this thesis provides the first comprehensive and statistically defensible data that these transformations do actually increase the photosynthesis and yield of a major food and feed crop under field conditions, and that these increases will not be diminished by rising atmospheric [CO2].
Issue Date: 2012-05-22
URI: http://hdl.handle.net/2142/30976
Rights Information: Copyright 2012 William Hay
Date Available in IDEALS: 2012-05-22
Date Deposited: 2012-05


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